The present invention relates to a semiconductor device and manufacturing method thereof, and particularly to effective technology applied to a semiconductor device having capacitive elements using an insulating film made from metallic oxide as a capacitive insulation film and a manufacturing method thereof.
In the related art, DRAMs (Dynamic random access memory) provided with transistors and capacitors are a typical example of a semiconductor storage device.
Capacitors constituting a DRAM are made of an upper electrode and a lower electrode, and a capacitive insulation film provided between these two electrodes. An insulation film made from a silicon compound such as a silicon oxide film or a nitride film is generally used as this capacitive insulation film Also at the present time, the use of high dielectric film or ferroelectric films, having smaller surface area but large capacitance compared to conventional capacitive insulation film made of silicon oxide or silicon nitride, as a capacitive film of a capacitor is being investigated.
Of these films, a capacitor having a ferroelectric film as a capacitive insulation film is used in the formation of semiconductor storage devices known as FeRAM (Ferroelectric random access memory).
FeRAM are non-volatile semiconductor storage devices capable of obtaining the same read speed and write speed as for a conventional DRAM. For this reason they are being noted as future semiconductor memory devices.
Insulating film made from metallic compounds, such as bismuth strontium titanate (SrBi2Ta2O9) called SBT or zirconium lead titanate called PZT, are used in capacitive insulating films of capacitors constituting a FeRAM. Also, precious metal such as platinum (Pt) is used in upper electrodes and lower electrodes constituting the capacitors. This is exposed to a high temperature oxidizing atmosphere at the time of forming the high strength dielectric film or at the time of membrane improvement of the capacitive insulation film after forming the capacitors, and therefore requires oxidation resistance for the electrode material.
Conventionally, a semiconductor storage device using this type of high strength dielectric film is formed by forming active elements on a semiconductor substrate, and then sequentially forming capacitors having a high strength dielectric film and wiring layers for electrical interconnection, through an interlayer insulation film.
However, with a strong dielectric film made from a metal oxide material included in a semiconductor storage device, such as FeRAM, the formation energy of the oxide material is low compared to a dielectric film formed from a silicon compound included in a conventional semiconductor storage device, and has the property that reduction is easy. Because of this, with formation of a plug for electrically connecting between an inter-layer insulation film and each wiring layer after formation of a capacitor, or a step of exposing a capacitor having a strong dielectric film, for preventing damage to semiconductor elements added in each process etc., to a reducing atmosphere, it is easy for the strong dielectric film to be reduced by hydrogen (H2) or moisture (H2O) contained in the reducing atmosphere. As a result, there are critical problems like deterioration in the film quality of the strong dielectric film, and also degradation to the electrical characteristics of the capacitor.
In a semiconductor storage device including a high strength dielectric film of the related art, a capacitor is used with a protective film for preventing diffusion of H2O from the reducing atmosphere formed on the surface.